• Journal of Advanced Marine Engineering and Technology
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• v.32 no.4
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• pp.570-577
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• 2008

Magnesium alloys are potentially useful as structural materials due to higher strength/weight ratio, heat conductivity and recyclability compared to other alloys. These alloys have attracted the interest of modern manufacturing such as the automobile, computer, communication and consumer electronic appliances industries. Hence welding techniques are required to be developed for these applications. Laser are known to be an excellent tool for them. This paper presents the laser weldability of AZ31 magnesium alloy with CW Nd:YAG laser. The low viscosity and surface tension of the melt pool make magnesium more difficult to weld than steel. As a result of this study, optimal process parameters could be obtained without weld defects. Also it was certain that cutting methods had influence on butt weldability.

• Journal of Welding and Joining
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• v.16 no.1
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• pp.106-113
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• 1998

In this study, the plug weldability of STS 304 was investigated. The parameters which influence plug weldability were pushing pressure of the plates, position of welding wire and composition of shielding gases. Among these factors, the composition of shielding gases and hole diameter of the upper plate were found to be the major factors influencing weld quality. To evaluate weldability, tensile shear strength of the plug welded specimen was measured and compared with tensile strength of butt welded specimen. Hardness was measured for both plug weld and butt weld. The microstructure of the weld metal and HAZ were also characterized.

• Journal of Welding and Joining
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• v.20 no.1
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• pp.55-61
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• 2002

The automobile is made up of about twenty thousand parts. Some parts are formed by pressing and combined by spot welding. Among them, steel palate of fuel tank is formed in the metal mold and bending parts are jointed by spot and seam welding. To find weldability conditions of spot welding, clearance between two welding steel plates was made and after spot welding, weldability is evaluated by means of tensile shear load, nugget size and shape. Specimen used in this study was a mild steel of 1.2mm thickness and electrode was Cu-Cr alloy of 6mm diameter. When spot welding started, the clearance of two steel plates was changed 0mm, 3mm and 5mm step by step. The fractured surface of specimen after this test was observed by Optical Microscope to measure microstructure and nugget shape. When clearance of two specimen was 3mm and 5mm, strength and nugget size was decreased and nugget shape was not clear.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.7
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• pp.78-84
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• 1998

The problem of autobody corrosion has been addressed over the past decade by the increasing use of zinc and zinc alloy coated steels in automotive application. This paper describes the evaluation of formability, weldability and painted corrosion performance of galvalume steel sheet. This paper presents an overview of the program and some initial test results on the weldability, lifetime of the electrode tip shape of the spot welding and corrosion protection. Galvalume steel sheet improved corrosion performance and spot weldability of galvalume steel sheet was not changed under the influence of the variation of welding current. And tip shape has influenced on the lifetime of tip for galvalume steel sheet.

• Journal of the Korean Society of Mechanical Technology
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• v.13 no.4
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• pp.143-148
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• 2011

This study analyzes the resistance spot weldability of DP60 steels. To analyze the resistance spot weldability of DP60 steels, tensile strength test and macro-section test were conducted for the resistance spot welds. Acceptable welding conditions were determined as a function of the resistance spot welding process parameters such as electrode force, welding time, and welding current. The lower limit of the welding lobe was the minimum shear tension strength for 590MPa-grade steel while the upper limit was determined whether or not expulsion was detected.

• International Journal of Korean Welding Society
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• v.3 no.1
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• pp.29-33
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• 2003

The ferritic stainless steels are generally considered to have poor weldability compared with that of the austenitic stainless steels. However the primary advantages of ferritic stainless steels include lower material cost than the more commonly used austenitic stainless steels and a greater resistance to stress corrosion cracking. Thus, the weldability of ferritic stainless steels was investigated in this study. In concerning the weldability, Grain size measurement test, Erichsen test and Varestraint test were involved. full penetration welds were produced by autogeneous direct current straight polarity (DCSP) and pulsed currents gas tungsten arc welding (GIAW) and the effect of pulsed currents welding on the welds was compared to that of DCSP welding. The results showed that pulsed current was effective to refine grain size in the weld metal and the finest grain size was obtained at the frequency of 150Hz. In addition, the ductility of welds was lower than that of base metal. Finally, autogeneous type 444 welds were less susceptible to macro solidification cracks, but more sensitive to micro cracks; SEM/EDS analysis indicated that all the inclusions in the crack showed enrichment of Mn, Si, O and S.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.626-631
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• 2002

This paper describes the weldability and mechanical behavior of JIS S45C medium carbon steel (corresponding to KS SM45C and SAE 1045) for machine structures in CW Nd:YAG laser welding. ill general, medium carbon steels have a limited application to the industrial fields in spite of good mechanical characteristics. This is due to welding difficulty because of the high carbon contents and impurities in this material. Therefore, in this study the laser weldability of medium carbon steel with adjusted contents of S and P has been investigated in order to extend the application to medium carbon steels. Several experiments and numerical simulations have been conducted to determine the characteristics of mechanical behavior in CW Nd:YAG laser welds. The results of the simulations concur with the experiment results. From the result of this study, the application possibility of CW Nd:YAG laser welding to medium carbon steel has been confirmed. Also, the appropriateness of mechanical behavior simulation has been verified to analyze and predict the welding phenomena.

• Journal of Welding and Joining
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• v.33 no.6
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• pp.21-26
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• 2015

Recently, application of UHSS(Ultra High Strength Steels) whose tensile strength is over 1000MPa to car body structure are growing due to great needs for light weighting and improved crash worthiness. However, their poor weldability is one of obstacles to expand selecting to car body. In this study, effect of Phosphorus contents on resistance spot weldability of high elongation DP980 steel whose Si content is over 1% was investigated. The cross tension strength (CTS) was decreased showing partial interface fracture as Phosphorus content increase because of solidification segregation of Phosphorus. In order to improve resistance spot weldability by modification of welding condition, in-situ post-weld heating pulse was introduced after main pulse. The optimum cooling time between main and post pulse and post-pulse current condtion were determined through FEM welding simulation and DOE tests. The CTS was increased about 1.5 time showing plug fracture. The decrease of Phosphorus segregation was found to be a major reason for weld ductility and CTS improvement.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.55-60
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• 2001

The automobile is made up of thousands of parts. Some parts are formed by pressing and combined by spot welding. To find weldability conditions of spot welding, clearance between two welding plates was made and after spot welding, weldability is evaluated by means of tensile shear load, nugget size and shape. Specimen used in this study was a steel plate of 1.2mm thickness and electrode was Cu-Cr alloy of 6mm diameter. When spot welding started, the clearance of two specimens was changed 0mm, 3mm and 5mm and distance from vise to measure influence of bending moment 25mm, 45mm, 65mm step by step. The fractured surface of specimen after this test was observed by Optical Microscope to measure microstructure and nugget shape. When clearance of two specimen was 3mm and 5mm, strength and nugget size was decreased and nugget shape was not clear. The much bending moment and crosshead speed are the much tensile shear load is.

• Journal of Welding and Joining
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• v.23 no.4
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• pp.59-65
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• 2005

The resistance spot welding is one of the most commonly used welding process for joining the sheet metal in automotive manufacturing process due to higher deposition rates and higher economy achieved. Control variables in the resistance spot welding for achieving high quality are welding current, welding force and welding time. Generally at the manufacturing scene, welding current Vs welding time lobe diagram is used to estimate weldability because controlling welding force is not practical due to economical reasons. However new automotive steel plates have been developed to make lightweight automobiles and to improve resistance against rusting. Also the weldability of these steel plates are worst than the existing steel plates because of changing bare metal and surface plating effect. In consequence of above mentioned reasons, it is necessary to use welding force to present the lobe diagram. In this study, we obtained the welding force Vs welding current lobe diagram for commonly used GA steel plate and found that the second order repression model of tensile shear strength was useful in reducing the number of experiments, and the indentation, and thickness change during welding were used as a response to estimate quantitatively expulsion.